It is well known for lubricating oils to contain a number of surface active additives (including antiwear agents, friction modifiers, dispersants, or detergents) used to protect internal combustion engines from corrosion, wear, soot deposits and acid build up. Often, such surface active additives can have harmful effects on engine component wear (in both iron and aluminium based components), bearing corrosion or fuel economy. A common antiwear additive for engine lubricating oils is zinc dialkyldithiophosphate (ZDDP). It is believed that ZDDP antiwear additives protect the engine by forming a protective film on metal surfaces. ZDDP may also have a detrimental impact on fuel economy and efficiency and copper corrosion. Consequently, engine lubricants may also contain a friction modifier to obviate the detrimental impact of ZDDP on fuel economy and corrosion inhibitors to obviate the detrimental impact of ZDDP on copper corrosion. Other additives may also increase lead corrosion.
Further, engine lubricants containing phosphorus compounds and sulphur have been shown to contribute in part to particulate emissions and emissions of other pollutants. In addition, sulphur and phosphorus tend to poison the catalysts used in catalytic converters, resulting in a reduction in performance of said catalysts.
With increasing control of both the formation of sulphated ash and release of emissions (typically to reduce NOx formation, SOx formation) there is a desire towards reduced amounts of sulphur, phosphorus and sulphated ash in engine oils. Consequently, the amounts of phosphorus-containing antiwear agents such as ZDDP, overbased detergents such as calcium or magnesium sulphonates and phenates have been reduced. As a consequence, ashless additives such as esters of polyhydric alcohols or hydroxyl containing acids including glycerol monooleate and alkoxylated amines have been contemplated to provide friction performance. However there have been observations that ashless friction modifiers may in some instances increase corrosion of metal, namely, copper or lead. Copper and lead corrosion may be from bearings and other metal engine components derived from alloys using copper or lead. Consequently, there is a need to reduce the amount of corrosion caused by ashless additives. However, reducing the levels of antiwear and other ash-containing additives may result in increasing amounts of wear and/or copper corrosion.
U.S. Pat. No. 3,127,349 discloses a composition optionally containing a nitrile ester capable of increasing the viscosity index of an oil containing a viscosity index improver and attenuating viscosity index decrease over time.
U.S. Pat. No. 3,366,569 discloses a composition resulting from contacting an alkylene polyamine with a hydrocarbyl substituted acylating agent and a nitrile such as acrylonitrile. The composition provides detergency and rust protection.
U.S. Pat. No. 4,025,446 discloses the use of several poly-nitrile compounds as effective anti-wear agents.
U.S. Pat. No. 4,209,408 discloses a lubricating composition containing at least one polyfunctional sulphur-containing nitrile.
U.S. Pat. Nos. 4,012,408 and 3,896,050 disclose a copper corrosion inhibitor derived from a cyano-substituted isothiazole.
U.S. Pat. No. 4,031,015 discloses oil-soluble compositions containing the reaction product of an olefin with an α,β-unsaturated nitrile to form an organonitrile. The organonitrile is then reacted with an amine or polyamine.
British Patent GB 1 538 889 discloses a lubricating composition containing a nitrile compound having either (i) an aliphatic thioether group, or (ii) an aliphatic ether group.
U.S. Pat. No. 4,058,469 discloses the use of polyfunctional nitriles as effective seal swelling agents and demulsifiers.
U.S. Patent Application 2006/0189489 A1 discloses a lubricating composition containing base oil, glycerol monooleate, and one or more nitriles.
U.S. Patent Application 2006/183652 discloses a lubricating composition containing base oil, oleylamide, an ether and at least one nitrile.
Romanian journal publication Revistade Chimie (Bucharest, Romania) (1981), 32(7), 686-7 discloses motor oil containing 0.5 wt % to 1 wt % of four nitriles as corrosion inhibitors, extreme pressure agents or antiwear agents. The nitriles include dodecylnitrile, stearylnitrile, oleylnitrile, and mixed-nitrile derivatives of linseed oil.
Canadian Patent CA 1 183 125 discloses lubricants for gasoline engines containing alkyl-ester tartrates, where the sum of carbon atoms on the alkyl groups is at least 8. The tartrates are disclosed as antiwear agents. Other references disclosing tartrates and/or tartrimides include International Publication WO 2006/044411, and US Patent Applications for internal combustion engines requiring reduced amounts of sulphur, sulphated ash, and phosphorus. The lubricant composition has anti-wear or anti-fatigue properties. The lubricating compositions are suitable for road vehicles.
U.S. Pat. No. 4,237,022 discloses tartrimides useful as additives in lubricants and fuels for effective reduction in squeal and friction as well as improvement in fuel economy.
U.S. Pat. No. 5,338,470 and International Publication WO 2005/087904 disclose lubricants containing at least one hydroxycarboxylic acid ester or hydroxy polycarboxylic acid (in particular citrates). The lubricant composition has anti-wear or anti-fatigue properties.
International Application WO2008/070307 discloses engine lubricants containing antiwear agents based on malonate esters.